This invention is concerned with anti-lubricant compositions, and relates in particular to such compositions which may be of use in the joint-producing methods described in our International Patent Application PCT/GB 91/00,950 (now published as WO 91/19,589) and a number of subsequent Applications.
In the Specification of the aforementioned PCT Application [P1220: Trib-joints] there is described and claimed a method of securing against lateral motion two bodies held in face to face asperity contact, thereby to make a join between the two bodies, in which method there is inserted into the interface between the two bodies a material that on minimal initial lateral relative motion of the two surfaces promotes rapid but controllable xe2x80x9cgallingxe2x80x9d between the two surfaces, this galling binding the surfaces against further such motion. The material inserted into the interface, and which causes the galling, is variously referred to as a galling agent, gall promoter, gall enhancer, or anti-lubricant, and the present invention relates to particularly preferred such anti-lubricants, and to compositions thereof. Variants of this are described in the Specification of our International Patent Application PCT/GB 93/00,046 (now published as WO 93/13,908) [P1284: Trib-bond].
The method of the two aforementioned Specifications is very suitable for joining bodies that fit well together, but not always so good at joining bodies that don""t, and in the Specification of our International Patent Application PCT/GB 94/00,869 (now published as WO 94/25,216) [P1286: Trib-paste] there is described and claimed another variant of the method, this variant being especially adapted for use with xe2x80x9cillxe2x80x9d-fitting jointsxe2x80x94that is, joints where it is thought that the two faces to be joined might not be in good face-to-face asperity contact, so there is a gap therebetweenxe2x80x94in which there is employed to fill the gap a composition comprising a multiplicity of small metal particles surrounded by or coated with a gall-promoting fluid that acts as a viscous binder.
In the aforementioned WO 91/19,589 and WO 93/13,908 Specifications the preferred described anti-lubricants are said generally to be liquid, especially such a material that appears in use to act as an oxygen scavenger when placed in contact with the material of the two bodies to be joined together. Typical examples of these materials are said to be the range of poly-dimethylsiloxane and polymethylhydrogensiloxane liquids of viscosities generally up to 100 c/s (volatile versions of similar siloxanes can be used where the surplus liquid that exudes from the joint naturally evaporates after the joint is formed). The same materials are identified in our aforementioned WO 94/25,216 Specification, while others are there described as being similar siloxanes but with amino active side groups that are able to cross link, or xe2x80x9cvulcanisexe2x80x9d, after the joint is made so as to form a synthetic rubber cocoon, and so prevent any small loose unbonded metal particles breaking loose in service.
Both the liquid anti-lubricant materials and the metal-particle-containing compositions of our aforementioned International Applications have proved satisfactory, but nevertheless there are occasions where the joint to be made is constructed from well-fitting parts, so that there is no need for the metal-filled viscous compositions of the latter, and yet the typically more liquid materials of the former are somewhat too fluidxe2x80x94or, rather, surface activexe2x80x94and tend to creep or even to flow out from their application site (which is not only wasteful of material, but means there is a risk of the anti-lubricant turning up where it is not wanted, which might even result in some damage being caused). It would seem that this dilemma might be solved by the provision of the anti-lubricant in the form of a composition that is a viscous fluid, a paste, a gel or even a semi-solid rubber-like material, and it is broadly this that the present invention proposes. More specifically, the invention suggests the use as the anti-lubricant of a composition of two or more siloxanes chemically reacted together to form a desirably thick viscous fluid, paste, gel or rubbery solid reaction product, the resultant reaction product being admixed with a more liquid, mobile siloxane that itself has anti-lubricant properties, this more mobile siloxane, which may be either one of the two reacted together or a completely different one, is immobilisedxe2x80x94stably dispersedxe2x80x94within the reaction product (and not only provides the required anti-lubricant property but may also be used to modify the final xe2x80x9cviscosityxe2x80x9d of the composition).
In one aspect, therefore, the invention provides a silicone composition having anti-lubricant properties and thus being of use in the promotion of galling between two gallable surfaces, the composition comprising a stable dispersion of a relatively mobile gall-promoting silicone xe2x80x9cimmobilisedxe2x80x9d within a matrix made of the cross-linked reaction product of at least two polyfunctional siloxanes and having the form of a viscous fluid, a paste, a gel or a rubbery solid.
The invention involves the utilisation of a silicone composition having anti-lubricant properties and thus being of use in the promoting of galling between two gallable surfaces. The concept of galling agents, anti-lubricants, and the promotion or enhancement of galling is well-known from our aforementioned Specifications, and needs no further comment at this time, save perhaps to summarise things by saying that certain types of metal joint, typically that having a form similar to a violin string tuning peg stuck in its hole in the scrolled end of the neck, can be made to bind together by material from one surface being transferred to the other, to make a lump rather like a gall (as seen on plants), this gall causing the joint surfaces to jam one onto the other, and to observe that gall formation can be promoted or enhanced by certain chemicals that seem to have the opposite effect to ordinary lubricants.
The composition of the invention contains the cross-linked reaction product of at least two different monomeric units each of which is itself a polyfunctional siloxane polymer (the product is thus a co-polymer). These materials are polyfunctional in that each contains at least two, and preferably at least three, functional groups (which may be the same or different) by which it can react with, and so attach itself to, the other to form a loose three-dimensional matrix capable of holding the relatively mobile gall-promoting silicone therewithin. Moreover, they are siloxanesxe2x80x94that is, they are themselves silicone polymers made up of many units derived from moieties of the type 
wherein R1 is an alkyl group, and R2 is the same or a different alkyl group (the preferred alkyl group R1 and R2 is the methyl group); these siloxane starting materials are themselves conveniently prepared by reacting corresponding compounds wherein some of the R groups are hydrogen with the donors of the required functional groups. The more useful starting siloxanes seem to be those of relatively limited reactivity, and those of relatively low molecular weight, and thus relatively short chain length (the number of the above moieties in each unit is conveniently, but not necessarily, from below 10 to above 300.
As to the functional groups, these can, within reason, be almost any set of groups capable of reacting one with another to form the desired polymeric product. One suitable pair of such groups is amine and dicarboxylic anhydride, 
which react together, two amine to one anhydride, to form amide linkages 
many of which will result in several molecules being cross-linked eventually to form a matrix having a complex dimensional structure.
Depending upon the polyfunctionality of the monomers chosen, the reaction product may be a linear polymer and yet, by virtue of the shape and 3D nature of the monomers, have a 2D or even 3D shape of its own, or it may be a 2D macromolecule, rather like a net, or a 3D macromolecule like a sponge. Moreover, even where the product is mostly sheet- or net-like, it may be interlinked so as to result in a loose three-dimensional structure. The problem is that determining the physical shape and structure of giant molecules such as these is extremely difficult, and at this time it is not easy to provide any information thereon except educated guesswork.
As will be apparent, the two (or more) polyfunctional siloxanes may have a wide variety of forms, but are preferably polydimethyl siloxanes with amino or anhydride functional groups. Most preferably they are of relatively low molecular weight (and thus have a relatively short chain length). Typical actual materials are the following:
Masil 28. This is a xe2x80x9chydrosiliconexe2x80x9d manufactured by Pittsburgh Plate Glass (PPG) Chemicals. It is believed to be a polydimethylsiloxane (with around 100-110 dimethylsiloxane monomer units) typically containing four active acid anhydride groups. It has a molecular weight of about 8,000, and a viscosity of around 130 c/s, and is said to be disclosed in PPG U.S. Pat. No: 4,876,152.
DC 536 This is made by Dow Corning. It is understood to be an amino, methoxy double-functional polydimethylsiloxane (with around 120-140 monomer units, molecular weight 9,000 and viscosity 160 c/s).
DC 109 Made by Dow Corning, this is thought to be a hydroxy-terminated polydimethyl siloxane (estimated chain length 600-650, molecular weight 47,000 and viscosity 4000 c/s).
DC 1107 Made by Dow Corning, this is a polymethyl-hydrogen siloxane (estimated chain length 30-35, molecular weight 2,600, viscosity 30 c/s).
Rhodorsil 1300 This is an amino functional material made by Rhone-Poulenc""s Spanish subsidiary Siliconas Hispania. It is understood to be a monoamine polydimethylsiloxane (chain length estimated to be 16-20, molecular weight 1,500, viscosity 14 c/s; amine content equivalent to 14,840 ppm N).
Rhodorsil Oil 21637 Another amino functional material from Rhone-Poulenc, believed to be a diamine polydimethylsiloxane (chain length estimated at 160-180, molecular weight 13,500, viscosity 300 c/s; amine content 4,200 ppm).
Rhodorsil Oil 21642 Another amino functional material from Rhone-Poulenc. It is thought to be a diamino polydimethylsiloxane (estimated chain length 340-360, molecular weight 27,000, viscosity 1,000 c/s; amino content 2,100 ppm).
Rhodorsil 48V100 to 1,000,000 A series of materials from Rhone-Poulenc. They are thought to be hydroxy-terminated polydimethylsiloxanes (estimated chain length 85-95, molecular weight 6,700, viscosity 100 c/s).
These, and other suitable materials, are shown in the following Table.
The siloxane reaction products used in the compositions of the inventionxe2x80x94that is to say, the reaction products themselves, as opposed to the compositions of the invention which use them together with a relatively-mobile gall-promoting siliconexe2x80x94are themselves novel materials, clearly of some usefulness, and the present invention extends to them per se. Thus, in another aspect the invention provides a polymeric silicone comprising the cross-linked reaction product of at least two polyfunctional siloxanes, wherein the polyfunctional siloxane polymers"" functional groups are respectively amine and anhydride groups, which react together, two amine to one anhydride, to form amide linkages. Of course, the invention also provides the processes described herein for the preparation of such silicones.
Because the gall-promoting capability of the anti-lubricant component may well involve some oxygen-scavenging effect, it is desirable if free oxygen can be kept away from the contacting surfaces of the joint being made using the compositions of the invention. This can be facilitated if the composition itselfxe2x80x94and specifically the reaction product matrix within which the anti-lubricant component is immobilizedxe2x80x94acts as a barrier to oxygen, and for that reason it may be advantageous to chooses the reaction product monomers, and thus the reaction product itself, with that capability in mind. As a guide, it has been found that in general the thicker or denser the composition the less room it has for adsorbed oxygen, and the less easily oxygen can subsequently be adsorbed thereinto.
The compositions of the invention may be the reaction product of more than two polyfunctional siloxanes, although at present the properties obtained from a reaction product which is of two (only) siloxanes is quite satisfactory.
The compositions of the invention comprise a stable dispersion of a relatively mobile gall-promoting, anti-lubricant silicone xe2x80x9cimmobilisedxe2x80x9d, or xe2x80x9cstoredxe2x80x9d, within a matrix made of the cross-linked reaction product of two (or more) polyfunctional siloxanes. It is quite possible for the relatively mobile anti-lubricant silicone to be one of the two (or more) siloxanes making up the reaction product matrix; many of these siloxanes are themselves good gall-promoters, and it is a simple matter to arrange that one such component be present in excess (of the stoichiometric amount necessary exactly to match the amount of-the other component(s)), this excess then becoming trapped within the matrix produced. However, it may be inconvenient to make a composition using as one of the two (or more) polyfunctional siloxanes a material that itself has anti-lubricant properties, and accordingly, and in a preferred aspect the invention""s anti-lubricant silicone composition are those wherein the relatively mobile gall-promoting silicone immobilised within a matrix made of the cross-linked reaction product is quite different from the siloxanes employed to make that reaction product.
A xe2x80x9cdifferentxe2x80x9d relatively-mobile anti-lubricant silicone may be almost any of the less viscous silicone/siloxanes previously mentioned as having gall-promoting, anti-lubricant properties (although of course some care should be taken, by simple preliminary tests, to ensure that this component is not incompatible with the reaction product matrix). The preferred siloxane generally suitable for this purpose is Dow Corning (DC) 1107 (a polymethylhydrogensiloxane having a viscosity of 30 c/s: it is mentioned in the Table hereinbefore), as well as DC 200/10 to 100 (these are a series of polydimethyl siloxanes having viscosities in the range 10 to 100 c/s); they are relatively inert and stable, probably because they have unreactive methyl side and end groups.
The amount of the more mobile anti-lubricant silicone that is employed will depend both on the degree of its anti-lubricant effect and on the ability of the reaction product matrix to hold the anti-lubricant (and on the ease with which the latter can be emplaced in the former). It may also depend on the exact physical form of composition requiredxe2x80x94whether it should be very viscous or only slightly so, whether it should be a stiff paste or a fairly runny one, whether it should be a solid, firm gel, even a xe2x80x9crubberyxe2x80x9d material, or a loose, easily-deformable onexe2x80x94for clearly the more anti-lubricant silicone is put into the matrix the more xe2x80x9cfluidxe2x80x9d the matrix is likely to become.
In general, the anti-lubricant effect of the more mobile silicone is sufficiently strong for only relatively small amounts to be necessary for that purposexe2x80x94perhaps as little as 5 to 10 vol % based on the reaction product. Moreover, in general the small amount required for giving the composition the desired anti-lubricant properties can always be mixed into, and held by, the reaction product matrix. However, the advantageous viscosity-adjusting effect of the more mobile silicone, which permits the preparation of compositions with a wide range of suitable physical forms, requires considerably more of the mobile silicone, and typical amounts are from 25 to 65 vol %, especially from 40 to 60 vol %, based on the total composition. With such large (proportional) amounts care should always be taken to match the mobile silicone to the matrix so that none, or only an acceptable amount at an acceptable rate, of the mobile silicone leaches out of the composition once it has been applied to the joint surface(s). It is not easy to give any specific directions on this, but it is so simple first to make small test quantities of composition and then to observe whether the mobile constituent separates out that it is not thought too onerous to suggest that the matter be decided on an individual test basis.
The xe2x80x9cthirdxe2x80x9d component of the compositions of the inventionxe2x80x94the relatively-mobile gall-promoting (or anti-lubricant) siliconexe2x80x94is physically immobilised within the matrix of the cross-linked reaction product. By this is meant in the first instance that the molecules of the anti-lubricant silicone are mechanically held, or trapped, within the structure of the reaction product (it should be noted, though, that many relatively mobile silicones usable as the anti-lubricant component have a limited chemical reactivity of their own, and may in time actually react with the matrix to become chemically bound therein as well as mechanically held thereby). For this holding to be most effectively achievable the siloxane reaction product is preferably the sort of chemically-linked substance that provides a 3D sponge-like xe2x80x9csupermoleculexe2x80x9d in which the anti-lubricant silicone component is secured so as to prevent it separating out (although in fact quite acceptable compositions have been prepared where the reaction product is thought to have more of a 2D, area-covering sheet-like form).
The anti-lubricant compositions of the invention contain the cross-linked reaction product of two polyfunctional siloxanes together with a gall-promoting silicone. The composition may have those components only, or it may include these constituents together with some other material. Classes of such additional material include thickeners (such as fumed silica), to make the composition more viscous (and perhaps paste- or gel-like, orxe2x80x94in the case of certain OH-terminated siloxane cross-linkersxe2x80x94even rubbery), as well as thinners (typically hydrocarbons like xylene and other, more mobile and fluid siloxanes), to make the composition less viscous.
The invention""s composition of cross-linked reaction product and anti-lubricant silicone is required to have the form of a viscous fluid, a paste, a gel or a rubbery solidxe2x80x94rather than, say, that of a mobile fluid or of a dense, rigid solidxe2x80x94in order that in use it will stay where it is put on the surface(s) to be joined. Any of these physical forms are acceptable; that chosen may depend upon the circumstances. Thus, the very viscous fluids are preferred for their ability to stay mostly where they are put and yet to ooze slowly into the intersurface areas of the joints they are to assist in making, and so ensure complete and uniform galling. The gelsxe2x80x94that is, compositions which have a jelly-like statexe2x80x94and especially those that exhibit non-Newtonian flow characteristics (particularly those that are thixotropic, being non-flowing when left alone but liquid-like when put under shear stress) are especially preferred because of their enhanced ability not to creep. It will be readily apparent that such gels can very conveniently be smeared over the surface(s) to be joined, and will stay unmoving on each until the two are put together to make the joint, whereupon as the shear forces applied mount the gel will flow into all the parts of the joint to initiate the best and most thorough galling.
Another preferred group is the rubbery solids, which can be useful in two quite separate ways. In one such way, the solid may simply be to increase the ease with which the anti-lubricant contained therein may be applied to the area where the galled joint is to be made (and when in place the two parts of the joint are rammed together to xe2x80x9csqueezexe2x80x9d the anti-lubricant out of the rubbery composition and into gall-promoting contact with the surfaces). In another, the solid may be formed as an item, like an O-ring, which is going to serve two different purposes, one to carry the anti-lubricant into place, and the other to effect some action by its very shape and texture (such as to seal the galled joint).
In this general connection it is convenient here to note that though as described hereinafter the compositions of the invention are made (in bulk), and by admixture of the several components, for storage followed by later use and application, the rubbery compositions of the invention have the added bonus that they can actually be formed in situ by reacting the components on the very surface where the composition is later to be employed. For example, if a gear wheel or bearing is to be affixed (by a galled joint) onto a shaft, the shaft itself can be xe2x80x9cpaintedxe2x80x9d with first one and then the other composition components, which are then allowed to react to produce a xe2x80x9cdryxe2x80x9d, though possibly slightly xe2x80x9ctackyxe2x80x9d surface coating that is the required stable composition in its rubbery form, and thereafterxe2x80x94possibly some considerable time thereafter (during which the shaft may be put away in store until it is required)xe2x80x94the mating parts can be slid along the shaft to engage the coated area and be xe2x80x9cgalledxe2x80x9d into place thereat.
It should be noted that these in situ rubbery compositions may stay in a xe2x80x9ctackyxe2x80x9d state for some considerable timexe2x80x94days, even weeksxe2x80x94and that even while they are like this the more mobile silicone therein should be held fully immobile (so preventing potentially dangerous xe2x80x9ccreepxe2x80x9d); this is a major advantage of the invention""s compositions.
It might be thought that, the cross-linked two-polyfunctional siloxane reaction product being itself some sort of silicone polymer, almost any type of siloxane would suffice for this material. This appears not to be the case; conventional high viscosity siloxanes are long-chain molecules which tangle with each-other to provide unusual and slow but persistent flow behaviour (an extreme example of this is seen in the so-called xe2x80x9csilicone puttyxe2x80x9d, and these long chain siloxanes themselves are inherently much less effective as anti-lubricants), and when more mobile, more surface-active short- and conventional long-chain siloxanes are blended in to provide the required anti-lubricant properties the resulting compositions suffer badly from xe2x80x9cpersistent creepxe2x80x9d as the individual long-chain molecules untangle and separate with time, and the more mobile constituents leach out. It seems, then, that for the compositions to be successful in preventing creep and leaching of the more mobile component the siloxane used needs to be the sort of chemically-linked substance that provides a 3D sponge-like xe2x80x9csupermoleculexe2x80x9d in which the several components are bound so as to prevent them separating out. However, an additional possibility, suggested by the behaviour of certain of the compositions of the invention, is that there are formed loose chemical bondsxe2x80x94probably polar bondsxe2x80x94to the surface on which the compositions are placed; compositions in which the reaction product is formed from an amino-functional siloxane reacting with an acid anhydride-functional siloxane contain carbo-silic-acid groupings, and it seems possible that their very high surface tension (and the accompanying disinclination to xe2x80x9ccreepxe2x80x9d across a substrate surface to which they are applied) is related to the manner in which these groupings can form loose bonds with the substrate.
The cross-linked reaction products used in the compositions of the invention may be made very simply by just mixing the several components together in the appropriate quantities, possibly with some suitable temperature control and perhapsxe2x80x94when using certain of the reaction product starting materials that are not too reactivexe2x80x94in the presence of some appropriate catalyst. Moreover, when making a composition containing as the anti-lubricant not an xe2x80x9cexcessxe2x80x9d of one of the monomers making the reaction product but a different, third, more mobile anti-lubricant silicone, this latter mayxe2x80x94depending on its actual chemical nature (some otherwise suitable mobile silicones may themselves react with one or other reaction product starting material, which may not be desirable)xe2x80x94either be admixed with the reaction product components before they are themselves mixed, so that the reaction takes place in the presence of the mobile silicone, which is incorporated into the reaction product as it forms, or after they are mixed, so that it is absorbed thereinto rather like water into a sponge. This mixing will normally be a bulk operation, and the formed composition will usually be transferred into suitable containers and then stored until required. Occasionally, though, the composition may desirably be made in situ, as described hereinbefore in connection with the rubbery compositions.
The compositions of the invention can, of course, include other components to improve or modify their effect, their physical state, or their ease of use. For example, were it considered desirable to use a composition to assist in the making of a joint between two ill-fitting parts it would be perfectly possible to incorporate into the composition a myriad of small metal particles in the manner proposed in our aforementioned published International Application WO 94/25,216) [P1286: Trib-paste] (and the resultant composition would then be similar to, though not the same as, one of that Application""s own compositions). Again, the compositions might contain some viscosity-modifying material, such as the well-known thickener fumed silica, to give it exactly the right viscosity characteristics. Yet again, the compositions might contain tiny quantities (many dyes are reactive!)xe2x80x94around 2 parts by weightxe2x80x94of some sort of colouring agentxe2x80x94typically a fluorescent dye such as Oil Red 21734 (a phenol-azo-naphthol material) or Oil Orange 15533 (a xanthene derivative)xe2x80x94to render more obvious, and more easily visible, the area of the joint""s surface(s) to which they have been applied.
Various Examples and Test Results are now given, though by way of illustration only, to show details of the invention.
A number of Examples are given below in the order (for convenience) of the number of constituents used in their formulation, ranging from two up to five. The Examples chosen represent some of each of the principle formulations for implementing the method of the invention. These are chosen as being representative of the huge range of possibilities, and there are many variations feasible within each type, all able to meet the objective below.
All the compositions were made and cured (where applicable) at room temperature in the open atmosphere, using a standard glass beaker with stainless steel spatula for hand-mixing. Generally, each composition took five minutes of vigorous stirring except where rapid cross-linking occurred (and these exceptions are noted).
The compositions were all tested (using one or other of the Tests described hereinafter), and the Test Results are displayed in the Table that follows the Examples, as are also some comparative Test Results for a typical unblended siloxane anti-lubricant (Dow Corning 1107).
The common objective in all the exemplified formulations is to provide a composition of a carrier that is a cross-linked matrix (in the form of a high viscosity fluid, a gel or a rubber) in which a low molecular weight, relatively mobile free anti-lubricant silicone is retained, trapped, and capable of wetting the (metal) surfaces to which the composition is applied. The carrier matrix must be able to hold the anti-lubricant silicone effectively indefinitely both in storage and in use without it leaching or creeping out beyond the area of deliberate application to a surface.